If y varies directly with x, and If y = 4 when x = 12, how do you find y when x = -24?

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Answer 1 · 2016-03-08T02:23:06

$y=-8$

If $y$ varies directly with $x$ , an equation to express this can be:

$y=mx$

$1$ . Since $y=4$ when $x=12$ , substitute the values into $y=mx$ to determine the value of $m$ .

$y=mx$

$4=m(12)$

$color(blue)(m=1/3)$

$2$ . With the value of $color(blue)m$ known, substitute $color(blue)m$ and $x=-24$ into $y=mx$ to determine the value of $y$ .

$y=color(blue)(1/3)x$

$y=color(blue)(1/3)(-24)$

$y=1/color(red)cancelcolor(black)(3)^1(-color(red)cancelcolor(black)(24)^8)$

$color(green)(y=-8)$

$:.$ , $y=-8$ when $x=-24$ .